This invention relates to compositions useful for modifying the properties of thermoplastic polymers such as polyvinyl chloride and to methods for making such compositions.
The use of polymeric materials to modify the impact properties of rigid polyvinyl chloride (PVC) is widely known. For example, the addition of polyacrylic resins, butadiene-containing polymers such as acrylonitrile butadiene styrene terpolymers (ABS) and methacrylate butadiene styrene terpolymers (MBS), and chlorinated polyethylene (CPE) resins to rigid PVC is known to increase the impact strength of PVC products such as house siding panels, vinyl window frames, electrical conduit, and blow molded PVC bottles. Impact modifiers are typically used in these applications at from 5 to about 15 parts by weight per 100 parts of PVC resin. The PVC resin typically used in these applications is classified as medium or high molecular weight.
In the case of impact modification of low molecular weight PVC resins, such as are used in injection molding applications, the melt viscosity of the impact modifying material is higher than that of the PVC resin. This fact can result in poor dispersion and broad particle-size distribution of the impact modifier with the effect of the PVC compounds having low impact strength. Some improvement in impact strength can be gained by increasing the amount of impact modifier in the compound but this is economically counter-productive. The purpose of this invention is to provide polymeric materials that will serve as efficient impact modifiers for PVC materials, particularly those materials based on low molecular weight PVC.